Roberts BluTune50 dab radio tuning knob faulty

[rh100605]

The symptoms are that all controls work but rotating the tuning knob for menu or station selection has no effect. Replacing the rotary control had no effect.

This radio although  made by Roberts uses the Imagination Technologies KINO4 DAB processor used in Pure radios such as the H3, H4 and H6
The controls use four Analogue to digital inputs on the KINO4 processor.
For example
2.5Volt ref--> 10k---> A to D input-- > 33 ohm --> switch to gnd --> 1.5k -- > switch to gnd -->2k switch to gnd -->2.2k switch to gnd -->4.7k switch to gnd --> 6.8k+12K  switch to gnd -->46k --> one side of tuning rotary control
and
2.5Volt ref--> 10k---> A to D input-- > 33 ohm --> switch to gnd --> 1.5k -- > switch to gnd -->2k switch to gnd -->2.2k switch to gnd -->4.7k switch to gnd -->  -->65k --> second side of tuning rotary control

The other two chains do the volume control
Measuring  the voltage on any switch should be 2.5Volt as normally no switch is closed. However one chain was at 1.34 V and getting progressively lower as the point of measurement moved away from the A to D input.

So a short low down the chain which I could not find on the removed switch boards. I then noticed on the mother board switch board socket a track led off to the display connector and when I removed the display connector 2.5 volts returned

The fault was a solder hair under one of the two Sleep switches in parallel at the bottom of the chain situated above the display! Reflowing the solder cured the problem and removed a 1K resistance across the switches
As this was at the bottom of one chain  only the rotary control was affected.